Answer Within A Minute II

Number Theory Level 1

What is the answer for 1+ 2 + 3 + 4 + 5 + 6 +7 + 8 ...... + 99 ?

The answer is 4950.

9 solutions

敬全钟
Mar 27, 2014

By using the sum of the first n consecutive numbers, we have $\frac{n(n+1)}{2}=\frac{99(100)}{2}=4950$

Indeed, the formula above came from this formula: $\frac{n}{2}(a+l)$ where n is the number of the terms in certain ARITHMETIC PROGRESSION (a sequence which satisfy $m_2-m_1=m_3-m_2.=...=m_{n+1}-m_n$ where $m_i$ are the terms in the sequence) and a is the first term and l is the last term.

敬全钟 - 7 years, 2 months ago

same as I did, liked!

Evan Lee - 7 years, 2 months ago

did the same thing.

Jaydeep Parsana - 6 years, 10 months ago

I also did this

Ahmed Obaiedallah - 6 years ago

Wenn Chuaan Lim
Mar 27, 2014

Count by using this method: [ 1 + 99 = 100 , 2 + 98 = 100 , 3 + 97 = 100 ] continuously until 49 + 51 = 100. Therefore you had already got 49 hundreds which is 4900, Then, add 50 into it and you will get 4950.